/* @(#)e_acosh.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 *
 */

#include "math.h"
#include "float.h"

static const double
one    = 1.0,
ln2    = 6.93147180559945286227e-01;  /* 0x3FE62E42, 0xFEFA39EF */

double
__ieee754_acosh(double x)
{
    double t;
    int hx;
    unsigned int lx;
    EXTRACT_WORDS(hx,lx,x);
    if(hx<0x3ff00000) {        /* x < 1 */
        return (x-x)/(x-x);
    } else if(hx >=0x41b00000) {    /* x > 2**28 */
        if(hx >=0x7ff00000) {    /* x is inf of NaN */
            return x+x;
        } else
        return __ieee754_log(x)+ln2;    /* acosh(huge)=log(2x) */
    } else if(((hx-0x3ff00000)|lx)==0) {
        return 0.0;            /* acosh(1) = 0 */
    } else if (hx > 0x40000000) {    /* 2**28 > x > 2 */
        t=x*x;
        return __ieee754_log(2.0*x-one/(x+sqrt(t-one)));
    } else {            /* 1<x<2 */
        t = x-one;
        return log1p(t+sqrt(2.0*t+t*t));
    }
}

double acosh(double x)
{
  return __ieee754_acosh(x);
}